Embodiments of the invention relate generally to Micro-Electro-Mechanical Systems (MEMS) switches and, more particularly, to MEMS switches having an anchor design that reduces the impact of any strain mismatch between the MEMS switch and the substrate on which the MEMS switch is mounted.
MEMS is a technology that in its most general form can be defined as miniaturized mechanical and electro-mechanical elements (i.e., devices and structures) that are made using the techniques of microfabrication. The critical physical dimensions of MEMS devices can vary from well below one micron on the lower end of the dimensional spectrum, all the way to several millimeters. Likewise, the types of MEMS devices can vary from relatively simple structures having no moving elements, to extremely complex electromechanical systems with multiple moving elements under the control of integrated microelectronics, with MEMS often acting as relays, for example (hereinafter referred to as “MEMS switches”).
With respect to MEMS switches, the one main criterion of MEMS switches is that there are at least some elements having some sort of mechanical functionality, whether or not these elements can move. Accordingly, MEMS switches generally include a moveable portion such as a cantilever, which has a first end anchored to a substrate (i.e., an “anchor”), and a second free end having a cantilever contact. When the MEMS switch is activated, the cantilever moves the cantilever contact against a substrate contact on the substrate and under the cantilever contact.
A problem of undesirable deformation of MEMS switches often occurs due to a significant difference in the coefficient of thermal expansion (CTE) between the metal comprising the MEMS switch and the semiconductor substrate, with it being recognized that the substrate includes numerous layers/materials such as a handle wafer, an insulator layer, a device layer, a metal-dielectric stack, and a passivation layer, for example. The CTE of the metal making up the MEMS switch often ranges from two to seven times larger than the CTE of the semiconductor substrate (e.g., of the insulator making up the passivation layer). At room temperature (i.e., 25° C.), the difference in the CTE does not present a problem; however, during manufacture, assembly, or operation of the MEMS switch, the temperature of the MEMS switch and the substrate structure 14 can exceed 300° C., with temperatures of 400° C.-700° C. not being uncommon, depending on the wafer bonding process employed.
Responsive to these high temperatures to which the MEMS switch is exposed to, the strain state of the MEMS switch may change—with the change in strain rate being due to the CTE mismatch as well as annealing of the MEMS film (due to several effects such as void reduction, grain growth, etch). The change in strain rate can lead to recoverable and non-recoverable deformations of the cantilever, with such deformation potentially causing the MEMS switch to become non-functional if severe enough in magnitude. That is, an adhesion between the cantilever contact and the substrate contact may prevent the cantilever contact and the substrate contact from breaking contact as the temperature of the MEMS switch decreases. A failure to break contact between the cantilever contact and the substrate contact will result in a failed MEMS switch, along with a failed product incorporating the MEMS switch. Furthermore, permanent deformation of the switch can result in altered switch performance beyond the acceptable operational range.
Prior attempts to solve this problem have been focused around minimizing the issues. For example, one solution has been to decrease the size of the region of the MEMS switch directly attached to the semiconductor substrate so as to minimize the strain-induced deflection of the cantilever. Another solution has been to decrease the size of the anchor in order to minimize the strain-induced deflection of the cantilever. However, such a reduction in the size of the anchor can lead to yield issues due to the difficulty in providing anchors of such size.
Therefore, it is desirable to provide a MEMS switch having a structure that is resistant to thermal actuation and deformation of the cantilever that might occur during manufacture, assembly, or operation of the MEMS switch. It is further desirable that such a MEMS switch be manufacturable at low cost while minimizing yield loss.